Move generator intro back in a method, so that generator context is available.

Also: Intro: the generator does not install the xtc module anymore.
Remove _config from xtc root. The config is created for the user by the generator.
Move generator intro back in a method, so that generator context is available.

Also: Intro: the generator does not install the xtc module anymore.
Validate git repository URI and allow empty string
Config: this should be a boolean, not a string.
Remove frontend/ and controllers/ from xtc root
Hm. what?